Nonaqueous Electrolyte Battery and Battery Pack

ABSTRACT

A nonaqueous electrolyte battery includes a positive electrode, a negative electrode and a nonaqueous electrolyte. The positive electrode contains active material particles and a coating material. The active material particles are represented by any one of the following formulae (1) to (3): 
       Li x M1 y O 2   (1)
 
       Li z M2 2w O 4   (2)
 
       Li s M3 t PO 4   (3)
 
     and have an average particle diameter of 0.1 to 10 μm. The coating material comprises at least particles having an average particle diameter of 60 nm or less or layers having an average thickness of 60 nm or less. The particles or the layers contain at least one element selected from the group consisting of Mg, Ti, Zr, Ba, B and C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/169,348, filed Jul. 8, 2008, which claims the benefit of, andpriority to, Japanese Patent Application No. 2007-183564, filed Jul. 12,2007, the entire contents of each of these applications beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a nonaqueous electrolyte battery and toa battery pack using a nonaqueous electrolyte battery.

2. Description of the Related Art

Nonaqueous electrolyte batteries using a negative electrode containing alithium metal, lithium alloy, lithium compound or carbonaceous materialare expected as high-energy-density batteries and are being exhaustivelyresearched and developed. Lithium ion batteries provided with a positiveelectrode containing LiCoO₂ or LiMn₂O₄ as an active material and with anegative electrode containing a carbonaceous material which absorbs andreleases lithium have been widely put to practical use so far. Also,with regard to the negative electrode, studies are being made as tometal oxides and alloys which are to be used in place of the abovecarbonaceous material. In the case of mounting a battery, particularly,in vehicles such as cars, materials superior in chemical andelectrochemical stability, strength and corrosion resistance are desiredas the structural material of the negative electrode to obtain a longcycle performance in a high-temperature environment and long reliabilityin high output. Moreover, it is demanded that batteries have highperformance in cold regions in the case of mounting them in vehiclessuch as cars. Specifically, it is required for these batteries to havehigh output performance and long-cycle life performance in alow-temperature environment. On the other hand, the development of anonvolatile and noninflammable electrolytic solution is underway toimprove safety performance. However, because such an electrolyticsolution brings about a deterioration in the output performance,low-temperature performance and long-cycle life performance of abattery, it has not been put to practical use yet.

Various trials have been made to improve the characteristics of anegative electrode. JP-A 2002-42889 (KOKAI) discloses that a negativeelectrode with a current collector made of aluminum or an aluminumalloy, which supports a specific metal, alloy or compound is used in anonaqueous electrolyte secondary battery. Also, JP-A 2004-296256 (KOKAI)discloses that an area where a negative electrode active material layeris not formed is disposed on the negative electrode current collectordescribed in the foregoing JP-A 2002-42889 (KOKAI) and this area is madeto face a positive electrode active material layer through a separatorto improve safety and reliability when a nonaqueous electrolytesecondary battery overcharges. Moreover, JP-A 2004-296256 (KOKAI) alsodiscloses that lithium-nickel-cobalt-aluminum oxide represented by theformula, LiNi_(0.8)Co_(0.8)Co_(0.15)Al_(0.05)O₂ is used as a positiveelectrode active material. As disclosed in JP-A 2004-296256 (KOKAI), ifa solid solution containing a heterogeneous element such as Al is usedas a positive electrode active material, the amount of lithium absorbedin the positive electrode active material is reduced.

In the meantime, JP-A 2001-143702 (KOKAI) discloses a method using, as anegative electrode active material, secondary particles obtained bycoagulating primary particles having an average particle diameter lessthan 1 μm which are made of a lithium titanate compound represented bythe formula, Li_(a)Ti_(3-a)O₄ (0<a<3), into granules having an averageparticle diameter of 5 to 100 μm, to thereby suppress the coagulation ofsecondary particles, thereby increasing the production yield of alarge-area negative electrode for large-size batteries.

Also, studies are made as to an improvement of a nonaqueous electrolyteto thereby attain low-temperature performance and high-temperature cyclelife performance at the same time. However, a nonaqueous electrolytehaving high ion conductivity at low temperatures tends to react easilywith a positive electrode at high temperatures, leading to remarkablyreduced cycle life performance.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda nonaqueous electrolyte battery comprising:

a positive electrode containing active material particles and a coatingmaterial which covers a surface of each of the active materialparticles, wherein the active material particles are represented by anyone of the following formulae (1) to (3) and have an average particlediameter of 0.1 to 10 μm, the coating material comprises at leastparticles having an average particle diameter of 60 nm or less or layershaving an average thickness of 60 nm or less, the particles or thelayers containing at least one element selected from the groupconsisting of Mg, Ti, Zr, Ba, B and C;

a negative electrode including a metal compound absorbing lithium ionsat 0.4 V (vs. Li/Li⁺) or more;

a separator interposed between the positive electrode and the negativeelectrode; and

a nonaqueous electrolyte including a mixture solvent and a lithium saltto be dissolved in the mixture solvent, the mixture solvent containing afirst nonaqueous solvent containing at least one of propylene carbonateand ethylene carbonate and a second nonaqueous solvent containing atleast one of γ-butyrolactone and a nonaqueous solvent having a nitrilegroup and a molecular weight of 40 to 100, and a content of the secondnonaqueous solvent in the mixture solvent being 10 to 70% by volume:

Li_(x)M1_(y)O₂  (1)

Li_(z)M2_(2w)O₄  (2)

Li_(s)M3_(t)PO₄  (3)

where M1, M2 and M3, which may be the same or different, respectivelyrepresent at least one element selected from the group consisting of Mn,Ni, Co and Fe, and x, y, z, w, s and t satisfy the followingrequirements: 0<x≦1.1, 0.8≦y≦1.1, 0<z≦1.1, 0.8≦w≦1.1, 0<s≦1.1 and0.8≦t≦1.1.

According to a second aspect of the present invention, there is provideda battery pack comprises a nonaqueous electrolyte battery, thenonaqueous electrolyte battery comprising:

a positive electrode containing active material particles and a coatingmaterial which covers a surface of each of the active materialparticles, wherein the active material particles are represented by anyone of the following formulae (1) to (3) and have an average particlediameter of 0.1 to 10 μm, the coating material comprises at leastparticles having an average particle diameter of 60 nm or less or layershaving an average thickness of 60 nm or less, the particles or thelayers containing at least one element selected from the groupconsisting of Mg, Ti, Zr, Ba, B and C;

a negative electrode including a metal compound absorbing lithium ionsat 0.4 V (vs. Li/Li⁺) or more;

a separator interposed between the positive electrode and the negativeelectrode; and

a nonaqueous electrolyte including a mixture solvent and a lithium saltto be dissolved in the mixture solvent, the mixture solvent containing afirst nonaqueous solvent containing at least one of propylene carbonateand ethylene carbonate and a second nonaqueous solvent containing atleast one of γ-butyrolactone and a nonaqueous solvent having a nitrilegroup and a molecular weight of 40 to 100, and a content of the secondnonaqueous solvent in the mixture solvent being 10 to 70% by volume:

Li_(x)M1_(y)O₂  (1)

Li_(z)M2_(2w)O₄  (2)

Li_(s)M3_(t)PO₄  (3)

where M1, M2 and M3, which may be the same or different, respectivelyrepresent at least one element selected from the group consisting of Mn,Ni, Co and Fe, and x, y, z, w, s and t satisfy the followingrequirements: 0<x≦1.1, 0.8≦y≦1.1, 0<z≦1.1, 0.8≦w≦1.1, 0<s≦1.1 and0.8≦t≦1.1.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a partially broken sectional view showing a nonaqueouselectrolyte battery according to a first embodiment;

FIG. 2 is an enlarged sectional view of an essential part of anelectrode group of a nonaqueous electrolyte battery shown in FIG. 1;

FIG. 3 is a partially broken perspective view showing another nonaqueouselectrolyte battery according to a first embodiment;

FIG. 4 is an explosion perspective view of a battery pack according to asecond embodiment;

FIG. 5 is a block diagram showing an electric circuit of a battery packof FIG. 4; and

FIG. 6 is an electronic microphotograph of a positive electrode activematerial used in a nonaqueous electrolyte battery of Example 1.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A nonaqueous electrolyte battery according to this embodiment comprisesthe structures shown in the following (A) to (C).

(A) The nonaqueous electrolyte contains a mixture solvent and a lithiumsalt to be dissolved in the mixture solvent. This mixture solventcontains a first nonaqueous solvent constituted of one or more ofpropylene carbonate (PC) and ethylene carbonate (EC) and a secondnonaqueous solvent constituted of one or more of γ-butyrolactone and anonaqueous solvent having a molecular weight of 40 to 100 and a nitrilegroup. The content of the second nonaqueous solvent in the mixturesolvent is 10 to 70% by volume.

(B) The positive electrode contains active material particles and acoating material which exists on the surface of each of the activematerial particles. The active material particles are represented by anyone of the following formulae (1) to (3) and have an average particlediameter of 0.1 to 10 μm. The coating material can be made of particleswhich contain at least one element selected from the group consisting ofMg, Ti, Zr, Ba, B and C and have an average particle diameter of 60 nmor less. Also, the coating material can be made of layers which containat least one element selected from the group consisting of Mg, Ti, Zr,Ba, B and C and have an average thickness of 60 nm or less. Further, thecoating material can be made of both of the particles and the layers.

Li_(x)M1_(y)O₂  (1)

Li_(z)M2_(2w)O₄  (2)

Li_(s)M3_(t)PO₄  (3)

Here, M1, M2 and M3, which may be the same or different, respectivelyrepresent at least one element selected from the group consisting of Mn,Ni, Co and Fe, and x, y, z, w, s and t satisfy the followingrequirements: 0<x≦1.1, 0.8≦y≦1.1, 0<z≦1.1, 0.8≦w≦1.1, 0<s≦1.1 and0.8≦t≦1.1. x, y, z, w, s and t are preferably in the following ranges:0<x≦1, 0.98≦y≦1.05, 0<z≦1, 0.98≦w≦1.05, 0<s≦1 and 0.98≦t≦1.05.

(C) The negative electrode contains a metal compound that absorbslithium ions at 0.4 V (vs. Li/Li⁺) or more.

The present invention is based on the finding that when the positiveelectrode described in the above (B) and the negative electrodedescribed in the above (C) are used, the nonaqueous electrolyte havingthe composition shown in the above (A) is limited in redox decompositionat high temperatures, to thereby make it possible to attainlow-temperature performance and high-temperature cycle life performanceat the same time.

The above nonaqueous solvent which has a nitrile group and a molecularweight of 40 to 100 and γ-butyrolactone respectively have a relativelysmall molecular weight and a high dielectric constant and thereforegreatly contribute to an improvement in the ionic conduction ability ofthe nonaqueous electrolyte. In the mixture solvent containing the secondnonaqueous solvent and first nonaqueous solvent constituted of the abovesolvent, the ratio of the second nonaqueous solvent is designed to be 10to 70% by volume, which remarkably improves large-current dischargeperformance and output performance in a wide temperature range from atemperature as low as about −40° C. to a temperature as high as about45° C. One factor for this is that a lithium salt having a highconcentration can be dissolved in the above mixture solvent even in alow-temperature environment. The ratio of the second nonaqueous solventin the mixture solvent is more preferably 50 to 67% by volume. Thisfurther improves the output performance of the battery in alow-temperature environment (for example, −40° C.).

This nonaqueous electrolyte has the excellent characteristics asmentioned above, whereas it easily undergoes oxidation decomposition andreduction decomposition at high temperatures and therefore deterioratesin high-temperature cycle life performance, failing to attain thelow-temperature performance and high-temperature performance at the sametime. Since the negative electrode described in the above (C) can limitthe reduction decomposition of the second solvent, it can decrease theformation of an insulating coating on the surface of the negativeelectrode. Then, the positive electrode described in the above (B) canlimit the oxidation decomposition reaction of the second solvent withoutdecreasing the effect of the negative electrode on the limitation to thereduction decomposition of the second solvent. Therefore, when thepositive and negative electrodes as described in the above (B) and (C)are used, the oxidation decomposition and reduction decomposition of thenonaqueous electrolyte having the composition described in the above (A)at high temperatures can be limited and therefore, a nonaqueouselectrolyte battery which is superior in both low-temperature outputperformance and high-temperature cycle life performance and is improvedin high-temperature storage performance can be attained.

Explanations will be given as to each member of the nonaqueouselectrolyte battery according to this embodiment.

1) Nonaqueous Electrolyte

The nonaqueous electrolyte has the structure explained in the above (A).

As the nonaqueous solvent having a nitrile group and a molecular weightof 40 or more and 100 or less, one or more nonaqueous solvents selectedfrom acetonitrile (AN), propionitrile (PN), methoxyacetonitrile (MAN)and 3-methoxypropionitrile (MPN) may be used. Because this brings aboutan increase in the lithium ion conduction ability of the nonaqueouselectrolyte under low temperature (for example, −40° C.) to hightemperature (for example 45° C.) environments, whereby the outputperformance of the battery can be more improved.

Also, when as the second nonaqueous solvent, one or more nonaqueoussolvents selected from the group consisting of γ-butyrolactone (GBL),propionitrile (PN), methoxyacetonitrile (MAN) and 3-methoxypropionitrile(MPN) are used, the vapor pressure of the nonaqueous electrolyte isreduced at high temperatures, making it possible to use a thin outerpackage such as a laminate film, which is suitable for the developmentof a thin type light-weight battery.

The mixture solvent may contain cyclic carbonates, chain carbonates suchas diethyl carbonate (DEC), dimethyl carbonate (DMC) and methyl ethylcarbonate, chain ethers such as dimethoxy ethane (DME) and diethoxyethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolan(DOX) and sulfolane (SL).

Examples of the lithium salt (lithium salt electrolyte) include lithiumperchlorate (LiClO₄), lithium hexafluorophosphate (LiPF₆), lithiumtetrafluoroborate (LiBF₄), lithium hexafluoroarsenate (LiAsF₆), lithiumtrifluoromethasulfonate (LiCF₃SO₃), bistrifluoromethylsulfonylimidelithium [LiN(CF₃SO₂)₂], LiN(C₂F₅SO₂)₂, Li(CF₃SO₂)₃C and LiB[(OCO)₂]₂.One or two or more types of electrolytes may be used. Among thesematerials, lithium tetrafluoroborate (LiBF₄) and LiB[(OCO)₂]₂ arepreferable. Lithium tetrafluoroborate (LiBF₄) is particularlypreferable. When the lithium salt contains LiBF₄, the concentration ofLiBF₄ in the mixture solvent is possible to be 1.5 mol/L or more,whereby the chemical stability of the second nonaqueous solvent isimproved and also the electric resistance of the film on the negativeelectrode can be decreased. As a result, the low-temperature outputperformance and cycle life performance of the battery can beoutstandingly improved.

The foregoing mixture solvent containing the first and second nonaqueoussolvents has a high dielectric constant though it has a low viscosityand therefore, a lithium salt having a high concentration may bedissolved and used. Accordingly, the concentration of the lithium saltin the mixture solvent is preferably in the range of 1.5 mol/L to 2.5mol/L. This ensures that high power can be drawn in a low-temperatureenvironment. When the concentration of the lithium salt is less than 1.5mol/L, the concentration of lithium ions at the boundary between thepositive electrode and the nonaqueous electrolyte when the batterydischarges under a large current sharply lowers and there is therefore aconcern that the power remarkably lowers. When the concentration of thelithium salt exceeds 2.5 mol/L on the other hand, the viscosity of thenonaqueous electrolyte is so high that the transfer speed of lithiumions is reduced and there is the possibility of a significant reductionin power.

As the nonaqueous electrolyte, besides a liquid electrolyte prepared bydissolving a lithium salt in a nonaqueous solvent, a gel electrolyteobtained by forming a complex of the foregoing liquid electrolyte and apolymer material or a solid electrolyte obtained by forming a complex ofa lithium salt and a polymer material may be used. Examples of thepolymer material include polyvinylidene fluoride (PVdF),polyacrylonitrile (PAN) and polyethylene oxide (PEO). Also, thenonaqueous electrolyte may contain a room temperature molten salt madeof a nonvolatile and noninflammable ionic liquid.

2) Negative Electrode

This negative electrode comprises a negative electrode current collectorand a negative electrode layer which is supported on one or bothsurfaces of the negative electrode current collector and contains anactive material, a conductive agent and a binder.

As the active material of the negative electrode, the metal compoundexplained in the above (C) is used. The reason why the lithium ionabsorbing potential of the metal compound is limited to 0.4 V (vs.Li/Li⁺) or more is explained below. Examples of the active material thatabsorbs lithium ions at a potential less than 0.4 V (vs. Li/Li⁺) includecarbonaceous materials and lithium metals. If these active materials areused, the reduction decomposition of the second solvent occurs and thebattery is deteriorated not only in output performance and charge anddischarge cycle performance but also in other performances. The upperlimit of the lithium ion absorbing potential is preferably 3 V (vs.Li/Li⁺) and more preferably 2 V (vs. Li/Li⁺).

The metal compound capable of absorbing lithium ions at a potentialrange of 0.4 to 3 V (vs. Li/Li⁺) is desirably metal oxides, metalsulfides or metal nitrides.

Examples of the metal oxides include lithium-titanium containingcomposite oxides such as titanium oxide and lithium-titanium oxide,tungsten oxides such as WO₃, amorphous tin oxides such asSnB_(0.4)P_(0.6)O_(3.1), tin-silicon oxides such as SnSiO₃ and siliconoxides such as SiO. Among these compounds, titanium oxides andlithium-titanium oxides are preferable. The use of theselithium-titanium oxide and titanium oxide prevents the second nonaqueoussolvent from reduction decomposition, which outstandingly improves thecycle life performance of the battery at high temperatures.

Examples of the lithium-titanium oxides include lithium titanate havinga spinel structure such as Li_(4+x)Ti₅O₁₂ (x varies in the range:−1≦x≦3, depending on a charge/discharge reaction) and lithium titanatehaving a ramsdellite structure such as Li_(2+y)Ti₃O₇ (y varies in therange: −1≦y≦3, depending on a charge/discharge reaction).

As the titanium oxide, those containing Li or no Li before charging maybe all used. Examples of titanium oxides containing no Li beforecharge/discharge operations, that is, in their synthesis includetitanium oxides such as TiO₂ and titanium composite oxides containing Tiand at least one element selected from the group consisting of P, V, Sn,Cu, Ni and Fe. TiO₂ is preferably one which is an anatase type, isheat-treated at a temperature of 300 to 500° C. and has lowcrystallinity. Examples of the titanium composite oxides includeTiO₂—P₂O₅, TiO₂—V₂O₅, TiO₂—P₂O₅—SnO₂ and TiO₂—P₂O₅-MeO (Me is at leastone element selected from the group consisting of Cu, Ni and Fe). Theabove titanium composite oxide preferably has low crystallinity and hasa microstructure in which a crystal phase and an amorphous phase coexistor an amorphous phase exists independently. When the titanium compositeoxide has such a microstructure, the cycle performance can beoutstandingly improved.

Examples of titanium oxides include Li_(a)TiO₂ (0≦a≦1.1).

Examples of the metal sulfides include titanium sulfide such as TiS₂,molybdenum sulfide such as MoS₂ and iron sulfide such as FeS, FeS₂ andLi_(x)FeS₂.

Examples of the metal nitrides include lithium-cobalt nitride such asL_(x)Co_(y)N (0<x<4, 0<y<0.5).

The average particle diameter of the metal compound is preferably 1 μmor less. When the average particle diameter exceeds 1 μm, there is aconcern that the nonaqueous electrolyte battery fails to obtain highoutput performance. However, when the average particle diameter issmall, this causes easy coagulation of particles, so that thedistribution of the nonaqueous electrolyte is inclined to the negativeelectrode and there is therefore a concern that the exhaustion of theelectrolyte at the positive electrode is caused and therefore, the lowerlimit of the particle diameter is desirably designed to be 0.001 μm.

The metal compound desirably has the average particle diameter of 1 μmor less and the specific surface area when it is measured by a BETmethod using N₂ adsorption in the range of 3 to 200 m²/g. This furtherimproves the affinity of the negative electrode to the nonaqueouselectrolyte.

The specific surface area of the negative electrode is desirably in therange of 3 to 50 m²/g. The specific surface area is more preferably inthe range of 5 to 50 m²/g. Here, the specific surface area of thenegative electrode means a surface area per 1 g of the negativeelectrode layer excluding the current collector. Also, the negativeelectrode layer is a porous layer which is supported on the currentcollector and includes a negative electrode active material, aconductive agent and a binder.

The porosity of the negative electrode excluding the current collectoris desirably designed to be in the range of 20 to 50%. This makespossible to obtain a negative electrode having high affinity to thenonaqueous electrolyte and a high density. The porosity is morepreferably in the range of 25 to 40%.

The negative electrode current collector is desirably an aluminum foilor an aluminum alloy foil. The thickness of the aluminum foil oraluminum alloy foil is preferably 20 μm or less and more preferably 15μm or less. The purity of the aluminum foil is preferably 99.99 mass %or more. As the aluminum alloys, alloys containing elements such asmagnesium, zinc and silicon are preferable. In the meantime, the contentof transition metals such as iron, copper, nickel and chromium in thenegative electrode current collector is desirably designed to be 100mass-ppm or less.

As the conductive agent, for example, carbon materials may be used.Examples of the carbon materials include acetylene black, carbon black,cokes, carbon fibers, graphite, aluminum powder and TiO. As theconductive agent, cokes which have an average particle diameter of 10 μmor less and are heat-treated at a temperature from 800° C. to 2000° C.,graphite, TiO powder and carbon fibers having an average fiber diameterof 1 μm or less are more preferable. The BET specific surface area ofthe above carbon material measured using N₂ adsorption is 10 m²/g ormore.

Examples of the binder include polytetrafluoro-ethylene (PTFE),polyvinylidene fluoride (PVdF), fluorine rubbers, styrene butadienerubber and core-shell binders.

The compounding ratio of the above negative electrode active material,conductive agent and binder is preferably as follows: the negativeelectrode active material: 80 to 95% by weight, the conductive agent: 3to 18% by weight and the binder: 2 to 7% by weight.

The negative electrode is manufactured, for example, by suspending theaforementioned negative electrode active material, conductive agent andbinder in a proper solvent and by applying this suspension to thecurrent collector, followed by drying and pressing under heating.

3) Positive Electrode

This positive electrode comprises a positive electrode currentcollector, and a positive electrode layer which is supported on one orboth surfaces of the positive electrode current collector and containsan active material, a conductive agent and a binder.

The active material of the positive electrode contains the activematerial particles and coating material which are explained in the above(B).

First, the active material particles represented by the formula (1) willbe explained. M1 is desirably at least one element selected from thegroup consisting of Mn, Ni and Co. More preferable examples of thepositive electrode active material include lithium-manganese compositeoxides such as Li_(x)MnO₂, lithium-nickel-cobalt composite oxides suchas Li_(x)Ni_(1-a)Co_(a)O₂ (0.1≦a≦0.5), lithium-cobalt composite oxidessuch as Li_(x)CoO₂, lithium-nickel-manganese-cobalt composite oxidessuch as Li_(x)Ni_(1-b-c)Mn_(b)Co_(c)O₂ (0.1≦b≦0.5, 0≦c≦0.5) andlithium-manganese-cobalt composite oxides such as Li_(x)Mn_(1-d)Co_(d)O₂(0.1≦d≦0.5). These compounds have high heat stability and ensure highsafety.

With regard to the active material particles represented by the formula(2), M2 is desirably at least one element selected from the groupconsisting of Mn and Ni. More preferable examples of the positiveelectrode active material include Li_(x)Mn₂O₄ and spinel typelithium-manganese-nickel composite oxides such as Li_(z)Mn_(2-e)Ni_(e)O₄(0.3≦e≦0.8). These compounds have high heat stability and ensure highsafety.

With regard to the active material particles represented by the formula(3), M3 is desirably at least one element selected from the groupconsisting of Fe, Mn and Co. More preferable examples of the positiveelectrode active material include lithium-phosphorous oxides having anolivine structure. Examples of the lithium-phosphorous oxide includeLi_(s)FePO₄, Li_(s)Fe_(1-f)Mn_(f)PO₄ (0≦f≦1), Li_(s)NiPO₄, andLi_(s)CoPO₄. These compounds have high heat stability and ensure highsafety.

Particularly, examples of the positive electrode active material whichis significantly improved in low-temperature output performance andhigh-temperature cycle life performance when the mixture solventexplained in the above (A) is used include Li_(x)CoO₂,Li_(x)Ni_(1-b-c)Mn_(b)Co_(c)O₂, Li_(z)Mn₂O₄, Li_(z)Mn_(2-e)Ni_(e)O₄ andLi_(s)FePO₄. This is because the growth of a film formed on the surfaceof the positive electrode is suppressed, so that the electric resistanceof the positive electrode is decreased. Also, the stability of thebattery in a high-temperature environment is improved, therebyremarkably improving storage stability.

The elements such as Mg, Ti, Zr, Ba and B are preferably adsorbed to thesurface of active material particles in the form of compound particlessuch as metal oxide particles and phosphorous oxide particles. Or, theforegoing element is preferably made into the form of compound layerssuch as metal oxide layers or phosphorous oxide layers to cover thesurface of the active material particles instead of being adsorbed inthe form of compound particles. Examples of the above metal oxidesinclude MgO, ZrO₂, TiO₂, BaO and B₂O₃. Examples of the above phosphorousoxides include Mg₃(PO₄)₂. As to C, carbon particles are preferablyadsorbed to the surface of the active material particles.

In the case of using particles (hereinafter referred to aselement-containing particles) containing at least one element selectedfrom the group consisting of Mg, Ti, Zr, Ba, B and C, the averageparticle diameter of the active material particles is designed to be 0.1μm or more and 10 μm or less and the average particle diameter of theelement-containing particles is designed to be 60 nm or less. If theaverage particle diameter of the element-containing particles is set to60 nm or less when the average particle diameter of the active materialparticles is less than 0.1 μm, a large part of the surface of the activematerial particles is coated with the element-containing particles andtherefore, the ability of the active material particles to absorb andrelease lithium ions is hindered by the element-containing particles,resulting in no improvement in performance. Also, if the averageparticle diameter of the element-containing particles is set to 60 nm orless when the average particle diameter of the active material particlesexceeds 10 μm, the element-containing particles are present sparsely onthe surface of the active material particles and therefore, the effectof suppressing the oxidation decomposition of the second nonaqueoussolvent is not obtained. When the average particle diameter of theactive material particles is designed to be from 0.1 μm to 10 μm and theaverage particle diameter of the element-containing particles isdesigned to be 60 nm or less, the oxidation decomposition reaction ofthe second nonaqueous solvent can be suppressed without hindering thepositive electrode active material from absorbing and releasing lithiumions. The lower limit of the average particle diameter of theelement-containing particles is desirably designed to be 0.1 nm in orderto obtain a satisfactory effect.

In the case of using the layers (hereinafter referred to aselement-containing layers) containing at least one element selected fromthe group consisting of Mg, Ti, Zr, Ba, B and C, the average particlediameter of the active material particles is designed to be 0.1 μm ormore and 10 μm or less and the average thickness of theelement-containing layers is designed to be 60 nm or less. If theaverage thickness of the element-containing layers is set to 60 nm orless when the average particle diameter of the active material particlesis less than 0.1 μm, the ratio of the thickness of theelement-containing layers to the size of the active material particlesis large and therefore, the ability of the active material particles toabsorb and release lithium ions is hindered by the element-containinglayers, resulting in no improvement in performance. Also, if the averagethickness of the element-containing layers is set to 60 nm or less whenthe average particle diameter of the active material particles exceeds10 μm, the ratio of the thickness of the element-containing layers tothe size of the active material particles is unsatisfactory andtherefore the oxidation decomposition of the second nonaqueous solventis not suppressed. When the average particle diameter of the activematerial particles is designed to be from 0.1 μm to 10 μm and theaverage thickness of the element-containing layers is designed to be 60nm or less, the oxidation decomposition reaction of the secondnonaqueous solvent can be suppressed without hindering the positiveelectrode active material from absorbing and releasing lithium ions. Thelower limit of the average thickness of the element-containing layers isdesirably designed to be 0.1 nm in order to obtain a satisfactoryeffect.

When the foregoing coating material is formed on the surface of each ofthe active material particles represented by the above formula (1) or(2), the reactivity of the positive electrode active material to thenonaqueous electrolyte can be lowered because the crystallinity of thecoating material is lower than that of the active material particles.This limits the oxidation decomposition reaction of the secondnonaqueous solvent. In this case, the element to be used in the coatingmaterial is preferably Mg, Ti, Zr, Ba or B. Particularly preferableelement is Mg and Ti.

When the coating material mentioned above is formed on each of theactive material particles represented by the formula (3), theelectroconductivity of the active material particles is improved, sothat the overvoltage of the positive electrode is reduced, and it istherefore possible to suppress the oxidation decomposition of the secondnonaqueous solvent and particularly, the oxidation decomposition of thesecond nonaqueous solvent during charging. In this case, C, Mg or Ti ispreferable as the element used for the coating material. Among theseelements, C is particularly preferable.

The weight of the coating material preferably corresponds to 0.001% byweight or more and 3% by weight or less of the total weight of theactive material particles and coating material. When the weight of thecoating material exceeds the above maximum value, this causes anincrease in the electric resistance at the boundary between the positiveelectrode and the nonaqueous electrolyte, leading to a deterioration inoutput performance and is therefore not preferred. Also, when the weightof the coating material is less than the above minimum value, this isnot preferred because the reactivity of the coating material with thenonaqueous electrolyte is increased in a high-temperature environment,bringing about a significant deterioration in cycle life performance.The weight ratio is more preferably 0.01 to 1% by weight.

The average particle diameter and average thickness of the activematerial particles, element-containing particles and element-containinglayers are found by TEM image observation and by the measurement ofelemental distribution image using EDX.

The positive electrode active material is obtained by dispersing theactive material particles in a solution containing at least one elementselected from the group consisting of Mg, Ti, Zr, Ba, B and C, followedby drying and by baking the dried dispersion at 400 to 800° C. As to thebaking atmosphere, the dried dispersion is baked in a reducingatmosphere when C is used as the element or in the air when elementsother than C is used.

Examples of the conductive agent include acetylene black, carbon blackand graphite.

Examples of the binder include polytetrafluoro-ethylene (PTFE),polyvinylidene fluoride (PVdF) and fluorine rubbers.

The compounding ratio of the above positive electrode active material,conductive agent and binder is preferably as follows: the positiveelectrode active material: 80 to 95% by weight, the conductive agent: 3to 19% by weight and the binder: 1 to 7% by weight.

The positive electrode is manufactured, for example, by suspending thepositive electrode active material, conductive agent and binder in aproper solvent and by applying this suspension to the current collectormade of an aluminum foil or an aluminum alloy foil, followed by dryingand pressing. The specific surface area of the positive electrode layeris measured by a BET method in the same manner as in the case of thenegative electrode and is preferably in the range of 0.1 to 2 m²/g.

The current collector is preferably made of an aluminum foil or analuminum alloy foil. The thickness of the current collector ispreferably 20 μm or less and more preferably 15μ or less.

4) Separator

A separator is provided between the positive electrode and the negativeelectrode. As the separator, a porous film, a nonwoven fabric or thelike may be used. Examples of its structural material include syntheticresins (polyolefins such as polyethylene and polypropylene) andcellulose. One or two or more structural materials may be used. Specificexamples of the separator include nonwoven fabrics made of syntheticresins, polyethylene porous films, polypropylene porous films andnonwoven fabrics made of celluloses.

5) Container

As the container receiving the positive electrode, negative electrodeand nonaqueous electrolyte, a metal container or laminate film containermay be used.

As the metal container, metallic cans which are made of aluminum, analuminum alloy, iron or stainless and have an angular shape or cylinderform may be used. Also, the plate thickness of the container isdesirably 0.5 mm or less and more preferably 0.3 mm or less.

Examples of the laminate film include multilayer films obtained bycoating an aluminum foil with a resin film. As the resin, a polymer suchas polypropylene (PP), polyethylene (PE), nylon and polyethyleneterephthalate (PET) may be used. Also, the thickness of the laminatefilm is preferably 0.2 mm or less. The purity of the aluminum foil ispreferably 99.5% or more.

The metallic can made of an aluminum alloy is preferably made of alloyswhich contain elements such as manganese, magnesium, zinc and siliconand have an aluminum purity of 99.8% or less. Because the strength ofthe metallic can made of an aluminum alloy is outstandingly increased,whereby the wall thickness of the can be decreased. As a result, a thin,light-weight and high power battery having excellent radiating abilitycan be attained.

The nonaqueous electrolyte battery according to this embodiment is shownin FIGS. 1 and 2.

As shown in FIG. 1, an electrode group 1 is received in a rectangularcylindrical metallic can 2. The electrode group 1 has a structure inwhich a separator 5 is interposed between a positive electrode 3 and anegative electrode 4, which is made to have a flat form and is coiledspirally. The electrode group 1 is formed by laminating the positiveelectrode 3 and negative electrode 4 through the separator 5 interposedtherebetween into a flat form, and then coiling these electrodesspirally followed by heating pressing. The nonaqueous electrolyte (notshown) is supported by the electrode group 1. A band-like positiveelectrode lead 6 is electrically connected to the positive electrode 3.On the other hand, a band-like negative electrode lead 7 is electricallyconnected to the negative electrode 4. The positive electrode lead 6 iselectrically connected to a positive electrode conductive tab 8 andthese two members constitute a positive electrode terminal. The negativeelectrode lead 7 is connected to a negative electrode conductive tab 9and these two members constitute a negative electrode terminal. A sealplate 10 made of a metal is secured to an opening part of the metalliccontainer 2 by welding or the like. The positive electrode conductivetab 8 and the negative electrode conductive tab 9 are respectively drawnto the outside from a drawing port provided in the seal plate 10. Theinside peripheral surface of each drawing port of the seal plate 10 iscoated with an insulation member 11 to avoid the development of shortcircuits caused by the contact between the positive electrode conductivetab 8 and the negative electrode conductive tab 9.

As shown in FIG. 2, the positive electrode 3 is constituted of apositive electrode current collector 3 a and a positive electrode layer3 b laminated on both surfaces of the positive electrode currentcollector 3 a. On the other hand, the negative electrode 4 isconstituted of a negative electrode current collector 4 a and a negativeelectrode layer 4 b laminated on both surfaces of the negative electrodecurrent collector 4 a. In the electrode group 1, the positive electrodelayer 3 b is made to face the negative electrode layer 4 b through theseparator 5 except for the start and end part of the coil as shown inFIG. 2. The end part of the positive electrode layer 3 b is projectedover the end part of the negative electrode 4 b at both end surfaces ofthe electrode group 1, perpendicular to a coil axis direction L. Inother words, the positive electrode layer 3 b covers the negativeelectrode layer 4 b through the separator 5. As a result, the potentialat the end part of the positive electrode layer 3 b becomes almost thesame as the potential at the center of the positive electrode 3 b whichfaces the negative electrode layer 4 b and therefore, such a phenomenonthat the end part of the positive electrode layer 3 b falls into anovercharge state is suppressed. This limits a reaction between apositive electrode active material contained in the end part of thepositive electrode layer 3 b and the nonaqueous electrolyte. When theend part of the negative electrode layer is projected over the end partof the positive electrode, that is, when the negative electrode layercovers the positive electrode layer, the positive electrode potential atthe end part of the positive electrode layer is affected by the negativeelectrode potential at the part of an unreacted negative electrode layerprojected over the positive electrode layer. Therefore, the potential atthe end part of the positive electrode layer is an overcharge state whenthe battery is made to fully charge, whereby the cycle life performanceof the battery is remarkably reduced. Accordingly, the area of thepositive electrode layer is desirably larger than that of the negativeelectrode layer. Moreover, it is desirable to constitute an electrodegroup by coiling or laminating the positive electrode layer, separatorand negative electrode layer in the condition that the positiveelectrode layer is made to face the negative electrode layer via theseparator and the positive electrode layer is projected over thenegative electrode layer.

The area ratio (Sp/Sn) of the area (Sp) of the positive electrode layerto the area (Sn) of the negative electrode layer is preferably in therange of 1.001 or more and 1.2 or less. When this area ratio exceeds theabove range, the effect of improving the high-temperature storageperformance is reduced, while the output density of the battery israther reduced. Also, when the area ratio is less than 1.001, thehigh-temperature storage performance of the battery is rapidly reduced.The area ratio is more preferably in the range of 1.01 to 1.1. Thelength ratio (Lp/Ln) of the width (Lp) of the positive electrode to thewidth (Ln) of the negative electrode is preferably in the range of 1.001to 1.1.

As is illustrated in FIG. 1, a container made of a laminate film may beused instead of using a metallic container. This example is shown inFIG. 3. In FIG. 3, the same members that are shown in FIG. 1 aredesignated by the same symbols and explanations of these members areomitted. As shown in FIG. 3, an electrode group 1 is received in alaminate film container 12 formed with heat seal parts on the threesides of the container. A positive electrode terminal 13 doubling as alead and a conductive tab is electrically connected to a positiveelectrode 3 of the electrode group 1. On the other hand, a negativeelectrode terminal 14 doubling as a lead and a conductive tab iselectrically connected to a negative electrode 4 of the electrode group1. Each end of the positive electrode terminal 13 and negative electrodeterminal 14 is drawn from a heat seal part of the short sides of acontainer 12.

It is to be noted that the shape of the electrode group is not limitedto the flat and spiral form as illustrated in FIGS. 1 and 3 but may be,for example, a cylindrical and spiral form or a laminate structure. Inthe case of using a laminate structure, a seat-like separator may beinterposed between the positive electrode and the negative electrode, ora positive electrode or a negative electrode may be received in abag-like separator and one electrode received in the bag-like separatormay be laminated alternately on the other electrode. Moreover, alaminate structure may be formed in which a separator is folded zigzagand a positive electrode and a negative electrode are alternatelyinserted between folded separator parts. In the case of an electrodegroup having a laminate structure, the end part of the positiveelectrode layer may be projected over the end part of the negativeelectrode layer on at least one side of the electrode group.

Second Embodiment

The battery pack according to the second embodiment comprises thenonaqueous electrolyte battery according to the first embodiment. Thenumber of nonaqueous electrolytes may be two or more. It is desirablethat the nonaqueous electrolyte battery according to the firstembodiment be used as a unit cell and each unit cell be connectedelectrically in series or in parallel to constitute a battery module. Anexample of the battery pack according to the second embodiment is shownin FIGS. 4 and 5.

A unit cell 21 in a battery pack shown in FIG. 4 is constituted from,for example, a flat type nonaqueous electrolyte battery shown in FIG. 3.However, the unit cell 21 is not limited to this flat type nonaqueouselectrolyte battery. A flat type nonaqueous electrolyte battery as shownin FIG. 1 may be used.

The plural unit cells 21 are stacked one upon the other in the thicknessdirection in a manner to align the protruding directions of the positiveelectrode terminals 13 and the negative electrode terminals 14. As shownin FIG. 5, the unit cells 21 are connected in series to form a batterymodule 22. The unit cells 21 forming the battery module 22 are madeintegral by using an adhesive tape 23 as shown in FIG. 4.

A printed wiring board 24 is arranged on the side surface of the batterymodule 22 toward which protrude the positive electrode terminals 13 andthe negative electrode terminals 14. As shown in FIG. 5, a thermistor25, a protective circuit 26 and a terminal 27 for current supply to theexternal equipment are connected to the printed wiring board 24.

As shown in FIGS. 4 and 5, a wiring 28 on the side of the positiveelectrodes of the battery module 22 is electrically connected to aconnector 29 on the side of the positive electrode of the protectivecircuit 26 mounted to the printed wiring board 24. On the other hand, awiring 30 on the side of the negative electrodes of the battery module22 is electrically connected to a connector 31 on the side of thenegative electrode of the protective circuit 26 mounted to the printedwiring board 24.

The thermistor 25 detects the temperature of the unit cell 21 andtransmits the detection signal to the protective circuit 26. Theprotective circuit 26 is capable of breaking a wiring 31 a on thepositive side and a wiring 31 b on the negative side, the wirings 31 aand 31 b being stretched between the protective circuit 26 and theterminal 27 for current supply to the external equipment. These wirings31 a and 31 b are broken by the protective circuit 26 under prescribedconditions including, for example, the conditions that the temperaturedetected by the thermistor is higher than a prescribed temperature, andthat the over-charging, over-discharging and over-current of the unitcell 21 have been detected. The detecting method is applied to the unitcells 21 or to the battery module 22. In the case of applying thedetecting method to each of the unit cells 21, it is possible to detectthe battery voltage, the positive electrode potential or the negativeelectrode potential. On the other hand, where the positive electrodepotential or the negative electrode potential is detected, lithium metalelectrodes used as reference electrodes are inserted into the unit cells21.

In the case of FIG. 5, a wiring 32 is connected to each of the unitcells 21 for detecting the voltage, and the detection signal istransmitted through these wirings 32 to the protective circuit 26.

Protective sheets 33 each formed of rubber or resin are arranged on thethree of the four sides of the battery module 22, though the protectivesheet 33 is not arranged on the side toward which protrude the positiveelectrode terminals 13 and the negative electrode terminals 14. Aprotective block 34 formed of rubber or resin is arranged in theclearance between the side surface of the battery module 22 and theprinted wiring board 24.

The battery module 22 is housed in a container 35 together with each ofthe protective sheets 33, the protective block 34 and the printed wiringboard 24. To be more specific, the protective sheets 33 are arrangedinside the two long sides of the container 35 and inside one short sideof the container 35. On the other hand, the printed wiring board 24 isarranged along that short side of the container 35 which is opposite tothe short side along which one of the protective sheets 33 is arranged.The battery module 22 is positioned within the space surrounded by thethree protective sheets 33 and the printed wiring board 24. Further, alid 36 is mounted to close the upper open edge of the container 35.

Incidentally, it is possible to use a thermally shrinkable tube in placeof the adhesive tape 23 for fixing the battery module 22. In this case,the protective sheets 33 are arranged on both sides of the batterymodule 22 and, after the thermally shrinkable tube is wound about theprotective sheets, the tube is thermally shrunk to fix the batterymodule 22.

The unit cells 21 shown in FIGS. 4 and 5 are connected in series.However, it is also possible to connect the unit cells 21 in parallel toincrease the cell capacity. Of course, it is possible to connect thebattery packs in series and in parallel.

Also, the embodiments of the battery pack can be changed appropriatelydepending on the use of the battery pack.

The battery pack of the second embodiment is preferably applied to useswhere cycle performance under a large current is desired. Specificexamples of the application of the battery pack include uses as powersources of digital cameras, and uses for vehicles such as two- tofour-wheel hybrid electric cars, two- to four-wheel electric cars,power-assisted bicycles and a rechargeable vacuum cleaner. The uses forvehicles are particularly preferable.

The present invention will be explained in detail by way of exampleswith reference to the drawings. However, the present invention is notlimited to the examples described below.

Example 1

Lithium-nickel-cobalt-manganese composite active material particleswhich had an average particle diameter shown in the following Table 1and a layer structure and is represented by the formula,LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ were prepared as active material particles.These active material particles were dispersed in an ethanol solution inwhich magnesium acetate (CH₃COO)₂Mg₄H₂O was dissolved, and then dried.The dried dispersion was baked at the temperature shown in Table 1, tothereby prepare a positive electrode active material having a structurein which magnesium oxide (represented by, for example, MgO, 0<x<1)microparticles are stuck to the surface of the active materialparticles. The average particle diameter of MgO_(x) particles and amountof MgO_(x) particles to be stuck are shown in the following Table 1. Anelectron microphotograph obtained when the positive electrode activematerial was observed using TEM-EDX is shown in FIG. 6. It can beconfirmed from FIG. 6 that Mg oxide was stuck granularly to the surfaceof the active material particles.

To the obtained positive electrode material were added a graphite powderas a conductive agent in an amount of 8% by weight based on the totalamount of the positive electrode and PVdF as a binder in an amount of 5%by weight based on the total amount of the positive electrode. Thesecomponents were dispersed in n-methylpyrrolidone (NMP) solvent toprepare a slurry. The obtained slurry was applied to both surfaces of a15-μm-thick aluminum foil (purity: 99%), which was then treated throughdrying and pressing processes to manufacture a positive electrode inwhich the coating amount on one surface was 12.8 mg/cm², the thicknessof the positive electrode layer on one surface was 43 μm and theelectrode density was 3.0 g/cm³. The specific surface area of thepositive electrode layer was 0.5 m²/g.

In the meantime, a lithium titanate (Li₄Ti₅O₁₂) powder having a spinelstructure, an average particle diameter of 0.3 μm, a BET specificsurface area of 15 m²/g and Li absorbing potential of 1.55 V (vs.Li/Li⁺), a cokes powder having an average particle diameter of 0.4 μmand a BET specific surface area of 50 m²/g, an acetylene black powderand PVdF which was a binder were formulated in a ratio by weight of90:6:2:2. These components were dispersed in a n-methylpyrrolidone (NMP)solvent and the dispersion was stirred at 1000 rpm for 2 hours by usinga ball mill, to prepare a slurry. The obtained slurry was applied to a15-μm-thick aluminum alloy foil (purity: 99.3%), followed by drying anda heating pressing process to manufacture a negative electrode in whichthe coating amount on one surface was 13 mg/cm², the thickness of thenegative electrode layer on one surface was 59 μm and the electrodedensity was 2.2 g/cm³. The porosity of the negative electrode excludingthe current collector was 35%. The BET specific surface area of thenegative electrode layer, that is, the surface area per 1 g of thenegative electrode layer was 10 m²/g.

A laser diffraction particle size analyzer (trade name: SALD-300,manufactured by Shimadzu Corporation) was used for the measurement ofthe particle diameter of the negative electrode active material. Afterplacing about 0.1 g of the sample in a beaker, a surfactant and 1 to 2mL of distilled water were added to the sample and thoroughly stirred,and the solution was injected into a stirring water vessel. The lightintensity distribution was measured 64 times at an interval of 2seconds, the particle size distribution data was analyzed to determinethe average particle diameter of the negative electrode active material.

The BET specific surface area of the negative electrode active materialand negative electrode were measured using N₂ adsorption in thefollowing condition.

1 g of the powdery negative electrode active material or two negativeelectrodes of 2×2 cm² were prepared by cutting as samples. As the BETspecific surface area measuring device, a device manufactured by YuasaIonics Inc. was used and nitrogen gas was used as the adsorption gas.

The porosity of the negative electrode was calculated as follows: thevolume of the negative electrode layer was compared with that of thenegative electrode layer obtained when its porosity was 0% and anincrease in volume from the volume of the negative electrode layerobtained when its porosity was 0% was regarded as a pore volume. Whenthe negative electrode layer was formed on both surfaces of the currentcollector, the volume of the negative electrode layer was the totalvolume of the negative electrode layers formed on both surfaces.

The obtained positive electrode and the negative electrode were cut insuch a manner that the electrode width Lp of the positive electrodelayer was 51 mm, the electrode width Ln of the negative electrode layerwas 50 mm, namely, Lp/Ln was 1.02 and the ratio (Sp/Sn) of the area ofthe positive electrode layer to the area of the negative electrode layerwas 1.05. A separator made of a polyethylene porous film 20 μm inthickness was interposed between the obtained positive and negativeelectrodes. Then, these electrodes with the separator were coiled andpressed into a flat form to obtain an electrode group. In the obtainedelectrode group, these electrode layers were disposed such that thepositive electrode layer covers the negative electrode via theseparator. The end part of the positive electrode layer projected overthe end part of the negative electrode at both end surfacesperpendicular to the coil axis of the electrode group. Then, theelectrode group was received in a container of a thin metal can made ofan aluminum alloy (Al purity: 99%) 0.25 mm in thickness.

2.0 mol/L of lithium tetrafluoroborate (LiBF₄) as electrolyte wasdissolved in a solvent prepared by mixing propylene carbonate (PC),γ-butyrolactone (GBL) and acetonitrile (AN) in a ratio by volume of30%:40%:30% to thereby prepare a liquid nonaqueous electrolyte(electrolytic solution). This nonaqueous electrolyte was injected intothe electrode group received in the container, to thereby manufacture athin type nonaqueous electrolyte battery having the structure shown inthe above FIG. 1 and a thickness of 4 mm, a width of 30 mm and a heightof 60 mm.

Examples 2 to 18

Thin type nonaqueous electrolyte batteries were manufactured in the samemanner as in Example 1 mentioned above except that the composition,form, average particle diameter, average thickness and sticking amountof the particles or layers, positive electrode active materialcomposition, the average particle diameter of the positive electrodeactive material, and the type of aqueous solution to be used to form theparticles or layers, baking temperature, the composition of thenonaqueous solvent and the area ratio of the positive electrode/thenegative electrode (Sp/Sn) were set to those shown in the followingTables 1 and 3.

Example 19

A thin type nonaqueous electrolyte battery was manufactured in the samemanner as in Example 1 except that Li_(0.1)TiO₂ having an averageparticle diameter of 0.1 μm, low crystallinity and a Li absorbingpotential of 1.5 V (vs. Li/Li⁺) was used as the negative electrodeactive material.

Example 20

A nonaqueous electrolyte battery was manufactured in the same manner asin Example 1 except that Li₂Ti₃O₇ having an average particle diameter of0.5 μm, a ramsdellite structure and a Li absorbing potential of 1.5 V(vs. Li/Li⁺) was used as the negative electrode active material.

Example 21

A nonaqueous electrolyte battery was manufactured in the same manner asin Example 1 except that a spinel type lithium-manganese-nickelcomposite oxide having the composition shown in Table 1 described belowas the particles of the positive electrode active material.

Comparative Examples 1 to 7

Thin type nonaqueous electrolyte batteries were manufactured in the samemanner as in Example 1 mentioned above except that the composition,form, average particle diameter, average thickness and sticking amountof the particles or layers, positive electrode active materialcomposition, the average particle diameter of the positive electrodeactive material, and the type of aqueous solution to be used to form theparticles or layers, baking temperature, the composition of thenonaqueous solvent and the area ratio of the positive electrode/thenegative electrode (Sp/Sn) were set to those shown in the followingTables 2 and 4.

Comparative Example 8

A thin type nonaqueous electrolyte battery was manufactured in the samemanner that was explained in the above Example 1 except that graphitehaving a Li absorbing potential of 0.2 V (vs. Li/Li⁺) was used as thenegative electrode material, the same positive electrode active materialas that used in Comparative Example 2 and the composition of thenonaqueous solvent and the area ratio (Sp/Sn) of the positive electrodeto the negative electrode were set to those shown in the following Table4.

Comparative Example 9

A thin type nonaqueous electrolyte battery was manufactured in the samemanner as in Example 1 except that a nonaqueous solvent having the samecomposition as that of Comparative Example 8 was used.

Comparative Example 10

A thin type nonaqueous electrolyte battery was manufactured in the samemanner as in Example 1 except that graphite was used as the negativeelectrode active material.

Comparative Example 11

A thin type nonaqueous electrolyte battery was manufactured in the samemanner as in Example 1 except that the MgO_(x) particles were not stuckto the surface of the positive electrode active material particles.

Each of the obtained nonaqueous electrolyte batteries was made to chargeup to 2.8 V at 25° C. at a constant current of 6 A for 6 minutes andthen made to discharge up to 1.5 V at a current of 0.12 A to measuredischarge capacity. Here, the battery obtained in Example 21 was made tocharge up to 3.4 V. A high-temperature cycle test was made in which acharge operation of charging up to 2.8 V at a constant current of 6 Afor 6 minutes and then, a discharge operation of discharging to 1.8 V ata constant current of 0.6 A were repeated at 45° C. The cycle life inthe cycle test made at 45° C. was defined as the number of cycles whenthe discharge capacity reached 80% of the initial capacity. Also, alow-temperature performance test was made in which the retentivecoefficient of capacity in a discharge operation carried out at −40° C.at a current of 0.6 A was measured. The capacity obtained in a dischargeoperation carried out at 25° C. at a current of 0.6 A was defined as 100to calculate each retentive coefficient of capacity.

Moreover, the retentive coefficient of capacity at 25° C. at a currentof 15 A was measured by the method described below.

The battery was made to charge up to 2.8 V at 25° C. at a constantcurrent of 6 A for 6 minutes and then made to discharge to 1.8 V at aconstant current of 15 A to measure the retentive coefficient ofcapacity. The capacity obtained in a discharge operation carried out ata current of 0.6 A was defined as 100 to calculate each retentivecoefficient of capacity. Here, the battery obtained in Example 21 wasmade to charge up to 3.4 V.

These results of measurement are shown in the following Tables 1 to 4.

TABLE 1 Composition Average Amount Average of the particle diameter toPositive electrode particle Baking particles or average adhere activematerial diameter temperature or layers Form thickness (nm) (wt % )composition (μm) Type of solution (° C.) Example 1 Mg oxide Layer 50 0.1LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 2 Mg oxideLayer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example3 Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O400 Example 4 Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3(CH₃COO)₂Mg₄H₂O 400 Example 5 Mg oxide Layer 50 0.1LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 6 C Granular30 0.05 LiFePO₄ 0.5 Aqueous oxalic acid solution 800 Example 7 CGranular 30 0.05 LiFePO₄ 0.5 Aqueous oxalic acid solution 800 Example 8Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400Example 9 Zr oxide Granular 50 0.1 LiCoO₂ 3 Zr[O(CH₂)₃CH₃]₄ 400 Example10 Mg oxide Layer 50 0.1 LiCoO₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 11 Mgoxide Layer 50 0.1 LiCoO₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 12 Ba oxideGranular 60 0.12 LiCoO₂ 3 (CH₃COO)₂Ba 400 Example 13 Ti oxide Granular60 0.12 LiCoO₂ 3 Ti[O(CH₂)₃CH₃]₄ 400 Example 14 B oxide Granular 10 0.02LiCoO₂ 3 Aqueous boric acid solution 600 Example 15 Mg oxide Layer 200.05 LiMn₂O₄ 5 (CH₃COO)₂Mg₄H₂O 400 Example 16 Mg oxide Layer 50 0.1LiMn₂O₄ 5 (CH₃COO)₂Mg₄H₂O 400 Example 17 Mg oxide Layer 50 0.1LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 18 Mg oxideLayer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example19 Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O400 Example 20 Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3(CH₃COO)₂Mg₄H₂O 400 Example 21 Zr oxide Layer 50 0.1LiNi_(0.5)Mn_(1.5)O₄ 5 Zr[O(CH₂)₃CH₃]₄ 400

TABLE 2 Composition Average Amount Average of the particle diameter toPositive electrode particle Baking particles or average adhere activematerial diameter Type of temperature or layers Form thickness (nm) (wt%) composition (μm) solution (° C.) Comparative — — — — LiCoO₂ 3 — —Example 1 Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — — Example2 Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — — Example 3Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — — Example 4Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — — Example 5Comparative — — — — LiCoO₂ 3 — — Example 6 Comparative — — — — LiCoO₂ 3— — Example 7 Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — —Example 8 Comparative Mg oxide Layer 50 0.1 LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂3 (CH₃COO)₂Mg₄H₂O 400 Example 9 Comparative Mg oxide Layer 50 0.1LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 (CH₃COO)₂Mg₄H₂O 400 Example 10Comparative — — — — LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ 3 — — Example 11

TABLE 3 25° C. 15A −40° C. Discharge retentive retentive Nonaqueoussolvent capacity at coefficient of coefficient of Cycle life atcomposition Sp/Sn 25° C. (mAh) capacity (%) capacity (%) 45° C. (times)Example 1 30% PC/40% GBL/30% AN 1.05 650 80 70 2000 Example 2 30% PC/40%GBL/30% PN 1.05 640 75 60 2000 Example 3 30% PC/40% GBL/30% MAN 1.05 63070 60 2300 Example 4 30% PC/70% MPN 1.05 620 70 65 2600 Example 5 30%PC/70% GBL 1.05 620 55 60 2800 Example 6 30% PC/70% AN 1.05 650 70 702000 Example 7 30% PC/70% MAN 1.05 650 60 60 2300 Example 8 90% PC/10%AN 1.05 650 30 30 2500 Example 9 30% EC/70% GBL 1.05 650 60 80 2000Example 10 30% EC/70% GBL 1.05 640 60 60 3000 Example 11 70% PC/30% AN1.05 620 40 70 2600 Example 12 30% EC/70% GBL 1.05 620 65 40 1800Example 13 30% EC/70% GBL 1.05 610 60 40 1800 Example 14 30% EC/70% GBL1.05 650 50 40 1200 Example 15 30% EC/70% GBL 1.05 630 65 50 1200Example 16 30% PC/40% GBL/30% AN 1.05 610 60 55 1000 Example 17 30%PC/40% GBL/30% AN 1.01 620 80 70 1500 Example 18 30% PC/40% GBL/30% AN1.10 650 80 70 2500 Example 19 30% PC/40% GBL/30% AN 1.05 670 60 50 1900Example 20 30% PC/40% GBL/30% AN 1.05 660 75 70 2600 Example 21 30%PC/30% EC/40% GBL 1.05 550 60 60 1500

TABLE 4 25° C. 15A −40° C. Discharge retentive retentive Nonaqueoussolvent capacity at coefficient of coefficient of Cycle life atcomposition Sp/Sn 25° C. (mAh) capacity (%) capacity (%) 45° C. (times)Comparative 100% GBL 0.95 400 40 35 100 Example 1 Comparative 100% AN1.0 300 60 40 50 Example 2 Comparative 100% MPN 0.95 400 30 40 100Example 3 Comparative 95% PC/5% AN 0.95 60 30 30 200 Example 4Comparative 30% EC/70% DEC 0.95 600 30 5 200 Example 5 Comparative 20%EC/80% AN 0.98 400 30 35 50 Example 6 Comparative 20% EC/80% MPN 0.95200 10 40 50 Example 7 Comparative 20% EC/80% GBL 0.95 50 0 5 10 Example8 Comparative 20% EC/80% GBL 1.05 400 40 30 150 Example 9 Comparative30% PC/40% GBL/30% AN 1.05 550 40 10 100 Example 10 Comparative 30%PC/40% GBL/30% AN 1.05 500 40 30 60 Example 11

As is clear from Tables 1 to 4, each nonaqueous electrolyte batteryobtained in Examples 1 to 21 was superior to those of ComparativeExamples 1 to 11 in discharge capacity in a low-temperature (−40° C.)environment, capacity retentive coefficient in a discharge operation ata current as large as 15 A and cycle performance. Particularly, eachnonaqueous electrolyte battery obtained in Examples 1 to 7, 9 to 11, 18and 20 was superior in any of discharge performance at −40° C.,large-current discharge characteristics at a current of 15 A andhigh-temperature (45° C.) cycle life performance. In the most preferablecombination, EC and GBL were used as the nonaqueous solvent, Li_(x)CoO₂was used as the positive electrode active material and a compoundcontaining Mg was used as the coating material. A nonaqueous electrolytebattery having such a combination was most superior in high-temperature(45° C.) cycle performance as indicated by Example 10.

Also, it can be understood from Comparative Examples 9 to 11 that if anyone of the nonaqueous solvent, positive electrode active material andnegative electrode active material is out of the aspect defined in thisembodiment, the battery has inferior performances.

The Li absorbing potential of the negative electrode active materialused in the above examples was measured using the method explainedbelow.

The negative electrode used in each example was cut into a size of 2cm×2 cm to make a working electrode. The working electrode and a counterelectrode made of a lithium metal foil of 2.2 cm×2.2 cm were made toface each other through a glass filter separator and a lithium metal wasinserted as a reference electrode in such a manner as to be in contactwith neither the working electrode nor the counter electrode. Theseelectrodes were received in a glass cell of a three pole type and eachof the working electrode, counter electrode and reference electrode wasconnected to a terminal of the glass cell. 1.5 M/L of lithiumtetrafluoroborate (LiBF₄) was dissolved in a solvent prepared by mixingethylene carbonate and γ-butyrolactone in a ratio by volume of 1:2 toprepare an electrolytic solution. 25 mL of this electrolytic solutionwas poured to allow the separator and electrodes to be impregnatedsufficiently and then, the glass container was sealed. The manufacturedglass cell was disposed in a 25° C. thermostat and was made to charge ata current density of 0.1 mA/cm² to measure the lithium ion absorbingpotential of the working electrode. In this case, the value of thelithium ion absorbing potential in the condition that the batterycharges up to 50% was defined as the lithium ion absorbing potential.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A nonaqueous electrolyte battery comprising: apositive electrode containing active material particles and a coatingmaterial which covers a surface of each of the active materialparticles, wherein the active material particles are represented by anyone of the following formulas (1) to (3) and have an average particlediameter of 0.1 to 10 μm, the coating material comprises at leastparticles having an average particle diameter of 60 nm or less or layershaving an average thickness of 60 nm or less, the particles or thelayers containing at least one element selected from the groupconsisting of Mg, Ti, Zr, Ba, B and C; a negative electrode including ametal compound absorbing lithium ions at 0.4 V (vs. Li/Li⁺) or more; aseparator interposed between the positive electrode and the negativeelectrode; and a nonaqueous electrolyte including a mixture solvent anda lithium salt to be dissolved in the mixture solvent, the mixturesolvent containing a first nonaqueous solvent containing at least one ofpropylene carbonate and ethylene carbonate and a second nonaqueoussolvent containing at least one of γ-butyrolactone and a nonaqueoussolvent having a nitrile group and a molecular weight of 40 to 100, anda content of the second nonaqueous solvent in the mixture solvent being10 to 70% by volume:Li_(x)M1_(y)O₂  (1)Li_(z)M2_(2w)O₄  (2)Li_(s)M3_(t)PO₄  (3) where M1, M2 and M3, which may be the same ordifferent, respectively represent at least one element selected from thegroup consisting of Mn, Ni, Co and Fe, and x, y, z, w, s and t satisfythe following requirements: 0<x≦1.1, 0.8≦y≦1.1, 0<z≦1.1, 0.8≦w≦1.1,0<s≦1.1 and 0.8≦t≦1.1.